Seal arrangement



Feb. 21, 1950 l. B. BENSEN 2,498,479

SEAL ARRANGEMENT Filed March 27, 1946 Inventor: 1201* B. Bensen,

bywbw His Attobney.

Patented Feb. 21, 1950 SEAL ARRANGEMENT Igor B. Bensen, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application March 27, 1946, Serial No. 657,572

2 Claims. 1

My invention relates to a seal adapted for use with evacuated electrical devices and it has for its primary object to provide a new and improved arrangement for sealing shafts adapted to be rotated.

In evacuated electrical equipment, such as elec tron microscopes and electron diffraction instruments, the problem arises of sealing a shaft, such as the shaft of a manipulator, which extends between regions of different pressures and is used for controlling equipment located in a region having a pressure condition different from that which exists at the location of the operator. In the past, complicated arrangements employing a Sylphon bellows have been employed with necessary restrictions on the degree of motion and control obtained. The desired characteristics of a seal for such equipment are that a minimum amount of servicing be required and that the seal, at the same time, be able to withstand high differences in pressure and be mechanically reliable for long periods of time. Accordingly, it is an object of my invention to provide a new and improved sealing arrangement to be used on apparatus employing differential pressures which is simple in construction andreliable in operation.

It is still another object of my invention to provide a new and improved sealing arrangement for a rotatable shaft which likewise functions as a thrust bearing.

It is still another object of my invention to provide a new and improved seal for apparatus employing difierential pressure which is substantially permanently lubricated.

It is an important feature of my present invention to seal a shaft which extends through a wall part having differential pressures on opposite sides and in which leakage paths are made .of extended length and re-entrant in character.

The novel features of my invention will be described with greater particularity in connection with the accompanying drawing and set forth in the accompanying claims. In the drawing, Fig. 1 is a side view, partly in longitudinal section, of an electron diffraction instrument which includes the sealing arrangement of my invention, and Fig. 2 is an enlarged sectional view of the manipulator employed in the apparatus of Fig. 1 and which incorporates my invention.

Referring now to Fig. l, I have illustrated there- 2 rial. Intermediatethe cathode I and the window 2 is located a focusing yoke 3 utilized for focusing a beam of electrons upon an object to be examined and which is supported by an object holder 4. The object holder 4 is located within a specimen chamber 5 and the position of the object with'respect to the beam of electrons is externally controlled by means of a manipulator 6. In this type of equipment, the exact construction of which is pointed out with greater particularity and claimed in my copending application, Serial No. 627,953, filed November 10, 1945, now Patent No. 2,483,872, issued October 4, 1949, an electron beam emitted from the cathode l is focused by the yoke 3 to impinge upon an object supported by the holder 4 and a diffraction pattern is obtained on the fluorescent window 2. The position of the specimen being studied relative to the beam is adjusted by means of the manipulator 6 through three mutually perpendicular directions, as well as two axes of rotation. A manipulator of this type is described in my copending application, Serial No. 627,952, filed November 10, 1945, now Patent No. 2,440,067.

A portion of the manipulator is shown in enlarged section in Fig. 2 and comprises a tubular shaft 1 which supports the object holder 4 and which is rotatable by means of a handle 8. The shaft 1 extends within the specimen chamber 5 and is supported from the top surface thereof by means of a Sylphon bellows 9 which is sealed around an opening in in the saidupper surface. The Sylphon bellows 9, in turn, at its upper end is sealed to a disk H which is adjustable in a vertical direction by means of thumb screw l2.

A shaft i 3' is provided which is coaxial with the shaft 7 to rotate the object holder 4 in the manner disclosed in my copendin'g application and control the angle of incidence of the electron beam on the specimen being examined. To this end, the shaft I3 is provided with an external knob M by means of which the shaft may be rotated.

In order that the shafts l and l 3 may be rotated without causing leakage between the atmosphere and the evacuated region within the electron diffraction instrument, I provide a sealing arrangement for both of the shafts which, in the case of the shaft 1, comprises a rubber gasket l5,

\ a disk ii of fibrous material, and a retaining ring I 1 which is fastened by means of screws I8 to the plate H. The plate II has formed in its upper surface a shoulder l9 which is adapted to receive the rubber gasket IS. A second shoulder 2|] is likewise formed in the upper surface of the plate II to receive a flange 2| which-is provided on the outer surface of the shaft I. Preferably, the shaft I is divided into upper and lower portions which .are joined together by means of a threaded por- 2| and shoulder 20 may have a machine flt. With such a flt, the cooperating members 20, 2! form a thrust bearing surface to counteract the pullof the vacuum on the shaft I. At the same time, the leakage pathacross the disk or wall part II is increased by the two changes in direction at the corners of the shoulder 20.

The gasket l5 preferably is formed of a synthetic rubber which is oil-proof in character so that the swelling which is common to natural rubber when in contact with oil is avoided. The central hole in the gasket I! which seals .the shaft I is cut somewhat smaller than the outer diameter of the shaft 1 so that the gasket bulges out when put on the shaft, as shown in Fig. 2. The fibrous disk It may comprise, for example, a felt washer and preferably is saturated with a light lubricant, such as a low pressure oil. In

this way, the fibrous disk It lubricates the shaft I and allows the rubber gasket l5 to slide along the outer surface of the shaft 8 under the action of the vacuum. Such sliding assures a self-sealing action of the gasket since it tends to compress tighter around the shaft as the force of the vacuum attempts to straighten it out. At the same time, the disk l6 protects the rubber gasket from oxidation and dust particles.

The retainer ring I1 is provided to clamp the outer edge of the rubber gasket as well as to hold down the entire assembly and protect the seal from mechanical damage.

The sealing arrangement for the shaft II at the upper portion of the shaft I preferably is constructed in'the same manner as that described above and corresponding parts have been identified byeorresponding reference numerals.

An important feature of my improved sealing arrangement is that the cooperating shoulder 20 and flange zLprovide a re-entrant path which extends below the rubber gasket l5 so that air, in order to pass from the atmosphere to the evacuated instrument, must pass through the seal made between the rubber gasket I 5 and the shaft I and around the flange 2i. Since the junction of the rubber with the shaft is sealed by the lubricant provided by saturated felt disk l6, extremely oil reliable sealing is obtained. A corollary feature of my improved construction is the bearing surface which ls provided against thrust of the shaft I due to the pull of the vacuum on the shaft. It is pointed out that, since the surfaces 20, 2| are machine fitted, a light lubrication is desirable at the point and suitable metal or graphite lubricant maybe employed for that purpose.

While I have described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modiflcations may be made without departing from the invention. I therefore aim in the appended claims to cover all. such changes and modifications as fall within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A seal for a rotatable shaft extending through a continuous wall having differential pressures upon opposite sides thereof, said wall including a shoulder formed in said wall and surrounding said shaft, a flange sealed to said shaft and having a machine fit in said shoulder on the higher pressure side thereof, a resilient gasket, fltted in a second shoulder of said wall, surrounding said shaft and overlying said flange and a portion of said wall cooperating with said flange, said gasket having an opening smaller than said shaft diameter and being caused to bulge up around said shaft in the high pressure direction, means for clamping said gasket to said wall along its outermost boundary in contact with said second shoulder.

2. An arrangement according to claim 1 further comprising means mounted on the high pressure side of said gasket for supplying lubricant to said shaft along its points of contact with said gasket. r

- IGOR B. BENSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES: PATENTS 

